Semiconductor devices are found in many products in the fields of entertainment, communications, networks, computers, and household markets. Semiconductor devices are also found in military, aviation, automotive, industrial controllers, and office equipment. The semiconductor devices perform a variety of electrical functions necessary for each of these applications.
The manufacture of semiconductor devices involves formation of a wafer having a plurality of die. Each semiconductor die contains hundreds or thousands of transistors and other active and passive devices performing a variety of electrical functions. For a given wafer, each die from the wafer typically performs the same electrical function. Front-end manufacturing generally refers to formation of the semiconductor devices on the wafer. The finished wafer has an active side containing the transistors and other active and passive components. Back-end manufacturing refers to cutting or singulating the finished wafer into the individual die and then packaging the die for structural support and environmental isolation.
One goal of semiconductor manufacturing is to produce a package suitable for faster, reliable, smaller, and higher-density integrated circuits (IC) at lower cost. Flip chip packages or wafer level chip scale packages (WLCSP) are ideally suited for ICs demanding high speed, high density, and greater pin count. Flip chip style packaging involves mounting the active side of the die face down toward a chip carrier substrate or printed circuit board (PCB). The electrical and mechanical interconnect between the active devices on the die and conduction tracks on the carrier substrate is achieved through a solder bump structure comprising a large number of conductive solder bumps or balls. The solder bumps are formed by reflow process applied to solder material deposited on contact pads, which are disposed on the semiconductor substrate. The solder bumps are then soldered to the carrier substrate. The flip chip semiconductor package provides a short electrical conduction path from the active devices on the die to the carrier substrate in order to reduce signal propagation, lower capacitance, and achieve overall better circuit performance.
Semiconductor devices are known to be susceptible to damage from electrostatic discharge (ESD). When electrostatic charges accumulate on a human body, a high static potential is formed with respect to ground. If the human body touches or comes in close proximity to any part of the IC, the static potential can discharge through the IC and inject large currents which can damage the active and passive circuits on the IC. If the breakdown voltage of the semiconductor device is exceeded, then the IC can be rendered defective well before its useful life expectancy.
In high frequency applications, such as radio frequency (RF) wireless communications, integrated passive devices (IPDs) are often contained within the semiconductor device. Examples of IPDs include resistors, capacitors, and inductors. A typical RF system requires multiple IPDs in one or more semiconductor packages to perform the necessary electrical functions.
One semiconductor design goal is to provide IPDs that have expanded electrical properties, such as greater capacitance or inductance. The classic capacitor has two electrode plates separated by an intermediate dielectric material. The capacitance of an IPD is a function of the area of the electrode plates, type of intermediate dielectric material, and thickness of the dielectric material. In the case of capacitor sensitivity to ESD, the breakdown voltage is a function of the thickness and strength of dielectric material. While reducing the thickness of the dielectric thin film has the advantage of increasing capacitance density and reducing the size of the capacitor, the thinner dielectric makes the capacitor more susceptible to damage from an ESD transient event. If ESD energy is discharged across an unprotected thin film capacitor, the device can be damaged.